processor type.

[John Baldwin]

On Friday 14 January 2005 02:43 am, Wilko Bulte wrote:
> On Thu, Jan 13, 2005 at 04:26:51PM -0800, David O'Brien wrote..
>
> > On Mon, Jan 10, 2005 at 08:16:06AM -0500, David Gilbert wrote:
> > > I see in the compiler lines crawling by that gcc is asked to optimize
> > > for 'EV5' while being compatible with 'EV4'.  My Alpha is an EV4 ---
> > > I'm wondering if I would see better performance with a different flag
> > > there, but the gcc manual doesn't even acknowledge the existance of
> > > the options that are in use, let alone the available options.
> >
> > It doens't???
> >
> > >From /usr/share/mk/bsd.cpu.mk:
> >
> >     . elif ${MACHINE_ARCH} == "alpha"
> >     _CPUCFLAGS = -mcpu=ev4 -mtune=ev5
> >
> > http://gcc.gnu.org/onlinedocs/gcc-3.4.3/gcc/DEC-Alpha-Options.html#DEC-Al
> >pha-Options clearly tells:
> >
> > -mcpu=cpu_type
> >     Set the instruction set and instruction scheduling parameters for
> >     machine type cpu_type. You can specify either the EV style name or
> >     the corresponding chip number. GCC supports scheduling parameters for
> >     the EV4, EV5 and EV6 family of processors.
> >
> > -mtune=cpu_type
> >     Set only the instruction scheduling parameters for machine type
> >     cpu_type. The instruction set is not changed.
> >
> >
> > That said, you should remove the -mtune=ev5 or change it to -mtune=ev4.
> > My guess is you won't notice a difference, but this this change will
> > produce the best code for your machine.
>
> Any idea how drastic -mtune=ev6 would change things on a DS10 (to name
> a random box ;-) ?
>
> Am I correct in assuming that -mcpu=ev4 will result in not using the BWX
> etc of the newer CPUs?  And that -mcpu=ev6 will result in code that does
> not run on anything older than EV6 due to missing instructions etc?

Yes.  Note that setting CPUTYPE in make.conf gets all the right flags set for 
you automagically.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org